1. FIELD OF THE INVENTION
The present invention relates to a camera comprising a battery check circuit capable of automatically measuring and displaying a voltage of a main power supply battery.
2. DESCRIPTION OF THE PRIOR ART
In recent compact cameras, in particular, compact 35 mm cameras, a battery is used not only for photometry and light emission of an electronic flash but also for driving a motor to perform a distance measurement operation and a film feed operation. In such cameras, if a loaded battery does not have a voltage exceeding a rated value, the camera cannot be used at all.
Therefore, in a camera having many automatic functions, a user must be able to check a voltage of a battery loaded in a camera. For this purpose, a battery check button is provided to almost all the cameras, or a so-called release switch is provided to an initial stroke of a release button to perform a battery check operation.
With this device solely, however, when a camera is not used for a long period of time, a user tends to forget to check a battery voltage. In this case, he or she often knows a battery voltage state immediately before a photographing operation, and if the voltage is below the rated value, replaces a battery in a flurry.
In particular, in a camera using AA type batteries as a power supply, since the batteries tend to be self discharged, if the camera is not used for a long period of time, the above case often occurs.
In order to solve the above problem, another camera is proposed wherein a sub power supply battery such as a lithium battery with a very stable voltage is incorporated in addition to the main power supply battery, and a battery check result of the main power supply battery is always displayed on, e.g., a liquid crystal display of a low current consumption type using the sub power supply battery.
However, since a battery check operation of the main power supply battery accompanies large current consumption, it must be intermittently executed at long time intervals. For this reason, even if the batteries are unloaded or are re-loaded in wrong polarities, a display state is not changed until the next battery check is performed.
Taking the above points into consideration, in a camera having a function of always displaying a voltage of a loaded main power supply battery on an external portion of the camera, or whether or not a battery is loaded with correct polarity must be discriminated. In addition, the camera must have a function of performing a battery check operation of the main power supply battery regardless of the time intervals to immediately display the check result when the battery is correctly loaded.